We present a temperature-induced sedimentation/dispersion transition of ionic vesicles in the system of alkyldimethylamine oxide hemihydrochloride (CnDMAO.1/2HCl) with a hydrocarbon chain length of 12-16 (n = 12,14, and 16) and sodium 2-naphthalenesulfonate (NaNphS). The temperature-sensitive sedimentation/dispersion of ionic vesicles took place around a temperature of 50 degrees C, which was weakly dependent on the alkyl chain length. The combined effect of the thermally induced dissociation of the counterions from the vesicle and a hydrogen bonding between the nonionic and the cationic head groups is likely to be responsible for this unique behavior. (c) 2004 Elsevier Inc. All rights reserved.